Particle beam inspection apparatus

ABSTRACT

An improved particle beam inspection apparatus, and more particularly, a particle beam inspection apparatus including an improved load lock unit is disclosed. An improved load lock system may comprise a plurality of supporting structures configured to support a wafer and a conditioning plate including a heat transfer element configured to adjust a temperature of the wafer. The load lock system may further comprise a gas vent configured to provide a gas between the conditioning plate and the wafer and a controller configured to assist with the control of the heat transfer element.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority of U.S. application 62/699,643, whichwas filed on Jul. 17, 2018; and of U.S. application 62/869,986, whichwas filed on Jul. 2, 2019; both of which are incorporated herein byreference in their entireties.

FIELD

The embodiments provided herein disclose a particle beam inspectionapparatus, and more particularly, a particle beam inspection apparatusincluding an improved load lock unit.

BACKGROUND

When manufacturing semiconductor integrated circuit (IC) chips, patterndefects and/or uninvited particles (residuals) inevitably appear on awafer and/or a mask during fabrication processes, thereby reducing theyield to a great degree. For example, uninvited particles may betroublesome for patterns with smaller critical feature dimensions, whichhave been adopted to meet the increasingly more advanced performancerequirements of IC chips.

Pattern inspection tools with a charged particle beam have been used todetect the defects or uninvited particles. These tools typically employa scanning electron microscope (SEM). In the SEM, a beam of primaryelectrons having a relatively high energy is decelerated to land on asample at a relatively low landing energy and is focused to form a probespot thereon. Due to this focused probe spot of primary electrons,secondary electrons will be generated from the surface. By scanning theprobe spot over the sample surface and collecting the secondaryelectrons, pattern inspection tools may obtain an image of the samplesurface.

During operation of an inspection tool, the wafer is typically held by awafer stage. The inspection tool may comprise a wafer positioning devicefor positioning the wafer stage and wafer relative to the e-beam. Thismay be used to position a target area on the wafer, i.e. an area to beinspected, in an operating range of the e-beam.

SUMMARY

The embodiments provided herein disclose a particle beam inspectionapparatus, and more particularly, a particle beam inspection apparatusincluding an improved load lock unit. In some embodiments, the improvedload lock system includes a plurality of supporting structuresconfigured to support a wafer and a first conditioning plate. The firstconditioning plate includes a first heat transfer element configured toadjust a temperature of the wafer. The improved load lock system alsoincludes a first gas vent configured to provide a gas between the firstconditioning plate and the wafer. Furthermore, the improved load locksystem includes a controller including a processor and a memory. Thecontroller is configured to assist with control of the first heattransfer element.

In some embodiments, a method of conducting a thermal conditioning of awafer in a load lock system is provided. The method includes loading awafer to a load lock chamber of a load lock system and pumping down theload lock chamber. The method further includes providing a gas to theload lock chamber. The method also includes enabling a first heattransfer element in a first conditioning plate to adjust a temperatureof the first conditioning plate for transferring heat through the gas tothe wafer.

In some embodiments, a non-transitory computer readable medium isprovided. The non-transitory computer readable medium includes a set ofinstructions that is executable by one or more processors of acontroller to cause the controller to perform a method conducting athermal conditioning of a wafer. The method includes instructing avacuum pump to pump down a load lock chamber of a load lock system aftera wafer is loaded into the load lock chamber. The method also includesinstructing a gas supply to provide a gas to the load lock chamber andinstructing a first heat transfer element in a first conditioning plateto adjust a temperature of the first conditioning plate for transferringheat through the gas to the wafer.

In some embodiments, a method of pumping down a load lock chamber isprovided. The method includes pumping a gas out of the load lock chamberwith a first vacuum pump configured to exhaust the gas to a firstexhaust system and pumping the gas out of the load lock chamber with asecond vacuum pump configured to exhaust the gas to a second exhaustsystem.

Other advantages of the present invention will become apparent from thefollowing description taken in conjunction with the accompanyingdrawings wherein are set forth, by way of illustration and example,certain embodiments of the present invention.

BRIEF DESCRIPTION OF FIGURES

The above and other aspects of the present disclosure will become moreapparent from the description of exemplary embodiments, taken inconjunction with the accompanying drawings.

FIG. 1A is a schematic diagram illustrating an exemplary chargedparticle beam inspection system, consistent with embodiments of thepresent disclosure.

FIG. 1B is a schematic diagram illustrating an exemplary wafer loadingsequence in the charged particle beam inspection system of FIG. 1A,consistent with embodiments of the present disclosure.

FIG. 1C is a schematic diagram illustrating an exemplary waferdeformation effect in a charged particle beam inspection system.

FIG. 2 is an exemplary graph showing a wafer temperature change overtime in a charged particle beam inspection system.

FIGS. 3A and 3B are schematic diagrams illustrating exemplary load locksystems, consistent with embodiments of the present disclosure.

FIG. 3C is an exemplary graph showing a wafer temperature change overtime during wafer temperature conditioning in a load lock system,consistent with embodiments of the present disclosure.

FIGS. 3D and 3E are schematic diagrams illustrating exemplary load locksystems, consistent with embodiments of the present disclosure.

FIG. 3F is an exemplary graph showing a change in the efficiency of heattransfer relative to the gas pressure level in a load lock system,consistent with embodiments of the present disclosure.

FIG. 4 is a schematic diagram of an exemplary pre-aligner in anequipment front end module (EFEM), consistent with embodiments of thepresent disclosure.

FIG. 5 is a schematic diagram illustrating an exemplary configuration ofa wafer conditioning system, consistent with embodiments of the presentdisclosure.

FIG. 6A is a schematic diagram illustrating an exemplary configurationof a wafer conditioning system, consistent with embodiments of thepresent disclosure.

FIG. 6B is a schematic diagram illustrating an exemplary supportingstructure of the wafer conditioning system of FIG. 6A, consistent withembodiments of the present disclosure.

FIG. 6C is an exemplary graph illustrating temperature changes duringconditioning process in a wafer conditioning system, consistent withembodiments of the present disclosure.

FIG. 6D is a schematic diagram illustrating an exemplary control circuitof a wafer conditioning system, consistent with embodiments of thepresent disclosure.

FIG. 7 is a flow chart illustrating an exemplary method for conditioninga wafer temperature, consistent with embodiments of the presentdisclosure.

FIGS. 8A and 8B are schematic diagrams illustrating an exemplary chargedparticle beam inspection system with a vacuum pump system, consistentwith embodiments of the present disclosure.

FIG. 9 is an exemplary graph illustrating a pressure change in a mainchamber of a charged particle beam inspection system, consistent withembodiments of the present disclosure.

FIG. 10 is a schematic diagram illustrating an exemplary chargedparticle beam inspection system with a vacuum pump system, consistentwith embodiments of the present disclosure.

FIG. 11 is a flow chart illustrating an exemplary method for controllingvacuum level of a load lock chamber of the charged particle beaminspection system of FIG. 10, consistent with embodiments of the presentdisclosure.

DETAILED DESCRIPTION

Reference will now be made in detail to exemplary embodiments, examplesof which are illustrated in the accompanying drawings. The followingdescription refers to the accompanying drawings in which the samenumbers in different drawings represent the same or similar elementsunless otherwise represented. The implementations set forth in thefollowing description of exemplary embodiments do not represent allimplementations consistent with the invention. Instead, they are merelyexamples of apparatuses and methods consistent with aspects related tothe invention as recited in the appended claims.

Electronic devices are constructed of circuits formed on a piece ofsilicon called a substrate. Many circuits may be formed together on thesame piece of silicon and are called integrated circuits or ICs. Thesize of these circuits has decreased dramatically so that many more ofthem can fit on the substrate. For example, an IC chip in a smart phonecan be as small as a thumbnail and yet may include over 2 billiontransistors, the size of each transistor being less than 1/1000th thesize of a human hair.

Making these extremely small ICs is a complex, time-consuming, andexpensive process, often involving hundreds of individual steps. Errorsin even one step have the potential to result in defects in the finishedIC rendering it useless. Thus, one goal of the manufacturing process isto avoid such defects to maximize the number of functional ICs made inthe process, that is, to improve the overall yield of the process.

One component of improving yield is monitoring the chip making processto ensure that it is producing a sufficient number of functionalintegrated circuits. One way to monitor the process is to inspect thechip circuit structures at various stages of their formation. Inspectioncan be carried out using a scanning electron microscope (SEM). An SEMcan be used to image these extremely small structures, in effect, takinga “picture” of the structures. The image can be used to determine if thestructure was formed properly and also if it was formed in the properlocation. If the structure is defective, then the process can beadjusted so the defect is less likely to occur again.

While high process yield is desirable in an IC chip manufacturingfacility, it is also essential to maintain a high wafer throughput,defined as the number of wafers processed per hour. High process yieldsand high wafer throughput can be impacted by the presence of defects,especially when there is operator intervention to review the defects.Thus, high throughput detection and identification of micro andnano-sized defects by inspection tools (such as a SEM) is essential formaintaining high yields and low cost.

One aspect of the present disclosure includes an improved load locksystem that increases the throughput of the overall inspection system.The improved load lock system prepares a wafer in a manner that speedsup the inspection process when compared to conventional particle beaminspection systems. For example, an operator, who is inspecting a waferusing the conventional particle beam inspection system, needs to waitfor the wafer to be temperature stabilized before starting theinspection. This temperature stabilization is required because the waferchanges size as the temperature changes, which causes elements on thewafer to move as the wafer expands or contracts. For example, FIG. 1Cshows that elements 180, 182, 184, and 186 can move to new locations170, 172, 174, and 178 as a wafer 160 expands due to the temperaturechange. And when the precision for inspecting a wafer is in nanometers,this change in location is substantial. Accordingly, for the operator toprecisely locate and inspect the elements on the wafer, the operatormust wait until the wafer temperature stabilizes.

The improved load lock system conditions the wafer so that itstemperature is close to a temperature of an inspection wafer stage thatwill hold the wafer. The improved load lock system can condition thewafer by including a conditioning plate that transfers heat to or fromthe wafer before it is placed onto the wafer stage. By conditioning thewafer before it is placed onto the wafer stage, the inspection can beginwith much less delay. Therefore, the operator can inspect more waferswithin a given period of time, thereby achieving an increasedthroughput.

Relative dimensions of components in drawings may be exaggerated forclarity. Within the following description of drawings the same or likereference numbers refer to the same or like components or entities, andonly the differences with respect to the individual embodiments aredescribed. As used herein, unless specifically stated otherwise, theterm “or” encompasses all possible combinations, except whereinfeasible. For example, if it is stated that a component may include Aor B, then, unless specifically stated otherwise or infeasible, thecomponent may include A, or B, or A and B. As a second example, if it isstated that a component may include A, B, or C, then, unlessspecifically stated otherwise or infeasible, the component may includeA, or B, or C, or A and B, or A and C, or B and C, or A and B and C.

Reference is now made to FIG. 1A, which is a schematic diagramillustrating an exemplary charged particle beam inspection system 100,consistent with embodiments of the present disclosure. As shown in FIG.1A, charged particle beam inspection system 100 includes a main chamber10, a load lock chamber 20, an electron beam tool 40, and an equipmentfront end module (EFEM) 30. Electron beam tool 40 is located within mainchamber 10. While the description and drawings are directed to anelectron beam, it is appreciated that the embodiments are not used tolimit the present invention to specific charged particles. It is furtherappreciated that electron beam tool 40 can be a single-beam tool thatutilizes a single electron beam or a multi-beam tool that utilizesmultiple electron beams.

EFEM 30 includes a first loading port 30 a and a second loading port 30b. EFEM 30 may include additional loading port(s). First loading port 30a and second loading port 30 b may, for example, receive wafer frontopening unified pods (FOUPs) that contain wafers (e.g., semiconductorwafers or wafers made of other material(s)) or samples to be inspected(wafers and samples are collectively referred to as “wafers” hereafter).One or more robot arms (e.g., the robotic arms shown in FIG. 1B) in EFEM30 transport the wafers to load lock chamber 20.

Load lock chamber 20 may be attached to main chamber 10 with a gatevalve (e.g., gate valve 26 of FIG. 1B) between the chambers. Load lockchamber 20 may include a sample holder (not shown) that can hold one ormore wafers. Load lock chamber 20 may also include a mechanical transferapparatus (e.g., robot arm 12 of FIG. 1B) to move wafers to and frommain chamber 10. Load lock chamber 20 may be connected to a load lockvacuum pump system (not shown), which removes gas molecules in load lockchamber 20 to reach a first pressure below the atmospheric pressure.After reaching the first pressure, one or more robot arms (shown in FIG.1B) transport the wafer from load lock chamber 20 to main chamber 10.Main chamber 10 is connected to a main chamber vacuum pump system (notshown), which removes gas molecules in main chamber 10 to reach a secondpressure below the first pressure. After reaching the second pressure,the wafer is subject to inspection by electron beam tool 40.

A controller 50 is electronically connected to electron beam tool 40.Controller 50 may be a computer configured to execute various controlsof charged particle beam inspection system 100. While controller 50 isshown in FIG. 1A as being outside of the structure that includes mainchamber 10, load lock chamber 20, and EFEM 30, it is appreciated thatcontroller 50 may be part of the structure. While the present disclosureprovides examples of main chamber 10 housing an electron beam inspectiontool, it should be noted that aspects of the disclosure in theirbroadest sense are not limited to a chamber housing an electron beaminspection tool. Rather, it is appreciated that the foregoing principlesmay also be applied to other tools that operate under the secondpressure.

Reference is now made to FIG. 1B, which is a schematic diagramillustrating an exemplary wafer loading sequence in charged particlebeam inspection system 100 of FIG. 1A, consistent with embodiments ofthe present disclosure. In some embodiments, charged particle beaminspection system 100 may include a robot arm 11 located in EFEM 30 anda robot arm 12 located in main chamber 10. In some embodiments, EFEM 30may also include a pre-aligner 60 configured to position a waferaccurately before transporting the wafer to load lock chamber 20.

In some embodiments, first loading port 30 a and second loading port 30b, for example, may receive wafer front opening unified pods (FOUPs)that contain wafers. Robot arm 11 in EFEM 30 may transport the wafersfrom any of the loading ports to pre-aligner 60 for assisting with thepositioning. Pre-aligner 60 may use mechanical or optical aligningmethods to position the wafers. After pre-alignment, robot arm 11 maytransport the wafers to load lock chamber 20.

After the wafers are transported to load lock chamber 20, a load lockvacuum pump (not shown) may remove gas molecules in load lock chamber 20to reach a first pressure below the atmospheric pressure. After reachingthe first pressure, a robot arm 12 may transport the wafer from loadlock chamber 20 to a wafer stage 80 of electron beam tool 40 in mainchamber 10. Main chamber 10 is connected to a main chamber vacuum pumpsystem (not shown), which removes gas molecules in main chamber 10 toreach a second pressure below the first pressure. After reaching thesecond pressure, the wafer may be subject to inspection by electron beamtool.

In some embodiments, main chamber 10 may include a parking station 70configured to temporarily store a wafer before inspection. For example,when the inspection of a first wafer is completed, the first wafer maybe unloaded from wafer stage 80, and then a robot arm 12 may transport asecond wafer from parking station 70 to wafer stage 80. Afterwards,robot arm 12 may transport a third wafer from load lock chamber 20 toparking station 70 to store the third wafer temporarily until theinspection for the second wafer is finished.

Reference is now made to FIG. 2, which is an exemplary graph showing awafer temperature change over time for a charged particle beaminspection system. The vertical axis represents temperature change, andthe horizontal axis represents passage of time. The graph shows that thewafer temperature changes over time while the wafer is processed throughmultiple stages of wafer load sequence. According to the exemplary datashown in FIG. 2, when a FOUP, containing wafers to be inspected, isloaded to first loading port 30 a or second loading port 30 b, thetemperature of the wafer is approximately 22.5 degrees.

After the wafer is transported to a load lock chamber, the wafertemperature sharply drops almost one degree when the load lock chamberis pumped down to a vacuum. This sudden temperature drop may be referredto as a pump-down effect. Subsequently, when the wafer is transportedand loaded onto the wafer stage, the wafer and the wafer stage may be atdifferent temperatures. For example, the graph in FIG. 2 shows that,when the wafer is loaded to wafer stage (annotated in FIG. 2 as 210),there may be roughly a 2.5-degree temperature difference between thewafer located in the load lock chamber (annotated in FIG. 2 as 220) andthe wafer stage located in the main chamber (annotated in FIG. 2 as230). Under such circumstances, heat transfer may occur between thewafer and the wafer stage, thereby resulting in a deformation (e.g. athermal expansion shown in FIG. 1C) of the wafer (or the wafer stage).While the wafer stage or wafer is undergoing a thermal deformation, theinspection of the target area may not be possible or may have a reducedaccuracy. Thus, to perform a more accurate inspection, the system waitsfor a significant period of time until the wafer temperature stabilizesbefore an inspection can commence. This waiting time reduces thethroughput of the inspection system.

An example of wafer stage for quicker temperature stabilization may befound in European Patent Application No. EP18174642.1, titled PARTICLEBEAM APPARATUS and filed on May 28, 2018, which is incorporated byreference in its entirety. Another way to cope with this longstabilization time is conditioning the wafer temperature by pre-heatingor pre-cooling the wafer to match the temperature of the wafer stagebefore the wafer is loaded onto the wafer stage. In such embodiments,the conditioning step may be performed while the previous wafer isinspected on the wafer stage, and therefore, the overall throughput ofthe inspection system may be increased compared to a system in which theconditioning is performed after the wafer is loaded onto the waferstage.

In some embodiments, the temperature conditioning function may beimplemented in a load lock chamber, which may provide throughputimprovement as well as flexibility for the future. If the temperatureconditioning of the wafer is performed in the load lock chamber, thewafer next in the pipeline can be loaded into load lock chamber while aninspection of previous wafer is in progress. In some examples, it iscalculated that, in this sequence, the maximum available time tocondition a wafer would be approximately 5-10 minutes, which is aboutthe minimum inspection time of a wafer with the shortest user case inscope now. Therefore, one of the advantages of performing the wafertemperature conditioning in the load lock chamber is that the waferconditioning time can be hidden under the inspection time because theconditioning of the next wafer and the inspection of the current wafercan occur simultaneously. This may improve the overall throughput of theparticle beam inspection system.

In some embodiments, a charged particle beam inspection system (such ascharged particle beam inspection system 100 of FIG. 1B) may include acoarse temperature conditioner and a fine temperature conditioner. Forexample, a pre-aligner (such as pre-aligner 60 of FIG. 1B) may include acoarse conditioner, while a load lock chamber (such as load lock chamber20) includes a fine conditioner. The coarse conditioner may conditionthe wafer from, for example, a coarse offset of 2 degrees to 500 mk,while the fine conditioner can condition the wafer from, for example, afine offset of 500 mK to 50 mK.

Reference is now made to FIG. 3A, which shows an exemplary load locksystem 300 a, consistent with embodiments of the present disclosure. Insome embodiments, load lock system 300 a may include a plurality ofsupporting structures 325 and a conditioning plate 315 configured totransfer heat to wafer 320. In other embodiments, conditioning plate 315may be configured to additionally or alternatively transfer heat fromwafer 320. Supporting structures 325, coupled to conditioning plate 315,may support wafer 320 such that there is a space between wafer 320 andconditioning plate 315. While it is appreciated that more efficient heattransfer may be achieved as wafer 320 is positioned closer toconditioning plate 315, in some embodiments, it may be desirable to havesufficient distance in between wafer 320 and conditioning plate 315 toprovide space for a robot arm to lift or transport wafer 320. In someembodiments, the distance between wafer 320 and conditioning plate 315may be in a range of 1.5 mm to 10 mm to provide space to accommodate avariety of robot arm sizes in lifting or transporting a wafer. In someembodiments, the distance between wafer 320 and conditioning plate 315may be in a range of 3 mm to 5 mm to provide space to accommodate acertain type of robot arms while providing more efficient heat transfer,without requiring a special treatment for robot arm transportation. Insome embodiments, a special mechanism for lifting wafer 320 may be used,allowing the distance to be narrower.

Furthermore, even if two supporting structures 325 are shown in FIG. 3A,it is appreciated that system 300 a may include any number of supportingstructures 325. In some embodiments, wafer 320 may be passively placedon top of supporting structures 325 without any means of active coupling(e.g. electrostatic clamping). In other embodiments, wafer 320 may beheld onto supporting structures 325 using an active holding mean, suchas electrostatic clamping.

Load lock system 300 a may include a load lock chamber 310, such as loadlock chamber 20 of FIG. 1A. In some embodiments, load lock chamber 310may be configured to change the internal pressure between atmosphericand vacuum. A pump, such as a turbo pump (not shown), may be connectedto load lock chamber 310 to maintain a vacuum level at an appropriatelevel for conditioning the temperature of wafer 320. It is appreciatedthat the pump may be a type of pump different from a turbo pump as longas the pump is suitable for establishing a vacuum in load lock chamber310.

In some embodiments, conditioning plate 315 may include a heat transferelement 340 configured to change the temperature of conditioning plate315; which in turn affect the temperature of wafer 320. Heat transferelement 340 may be coupled to a heater/cooler 360. In some embodiments,heater/cooler 360 may be placed outside of load lock chamber 310. Inother embodiments, heater/cooler 360 may be placed inside of load lockchamber 310.

Load lock system 300 a may further include a controller 350 configuredto adjust heater/cooler 360 or heat transfer element 340 to change thetemperature of conditioning plate 315, which in turn affects thetemperature of wafer 320. In some embodiments, controller 350 mayreceive a stage-temperature data about the temperature of wafer stage395 in a main chamber 390. For example, in some embodiments, controller350 may receive an electric signal conveying the stage-temperature datafrom a temperature sensor 396 configured to measure the temperature ofwafer stage 395. In such embodiments, controller 350 may controlheater/cooler 360 to adjust the temperature of conditioning plate 315based on the stage-temperature data about the temperature of wafer stage395.

In some embodiments, controller 350 may receive a heater-temperaturedata about the temperature of output of heater/cooler 360. In suchembodiments, controller 350 may control heater/cooler 360 to adjust thetemperature of conditioning plate 315 based on the heater-temperaturedata. For example, in some embodiments, heater/cooler 360 may be a waterheater or water cooler. In such embodiments, heated or cooled waterflows through heat transfer elements 340 in conditioning plate 315, andcontroller 350 may receive the heater-temperature data about thetemperature of water at the output of heater/cooler 360. Controller 350may adjust heater/cooler 360 based on the water temperature. In someembodiments, controller 350 may receive an electric signal conveying theheater-temperature data from a temperature sensor 365 configured tomeasure the temperature of water. In some embodiments, controller 350may use both stage-temperature data and heater-temperature data toadjust the temperature of conditioning plate 315. In such embodiments,for example, controller 350 may adjust heater/cooler 360 to match theheater temperature (e.g. water temperature at the output ofheater/cooler 360) to the temperature of wafer stage 395.

In some embodiments, controller 350 may be further optimized withadditional temperature sensors. For example, in some embodiments, systemmay include one or more additional sensors configured to measure thetemperature of wafer 320 and conditioning plate 315.

In some embodiments, load lock system 300 a may include one or more gasvents (e.g., gas vents 330 or 335) to feed gas 338 from a gas supplyinto load lock chamber 310. In such embodiments, gas 338 may increasethermal conduction between wafer 320 and conditioning plate 315,resulting in a reduced time for wafer 320 to reach the stabletemperature. For example, heat transfer between wafer 320 andconditioning plate 315 may be created by radiation and gas 338. Gas 338may be nitrogen, helium, hydrogen, argon, CO2, or compressed dry air. Itis appreciated that gas 338 may be any other gas suitable for heattransfer. There may be valves 370 and 375 located between the gas supplyand load lock chamber 310. Gas vents 330 and 335 may be connected to gassupply through gas tubes running from the gas supply to vents 330 and335, which may be opened into load lock chamber 310 to provide gasbetween wafer 320 and conditioning plate 315. In some embodiments, gasvents 330 and 335 may be opened after load lock chamber is pumped downto vacuum level. In some embodiments, while gas 338 is supplied intoload lock chamber 310, the load lock vacuum pump (e.g. turbo pump) maybe enabled to continuously remove some of gas 338 molecules and maintainthe vacuum level during wafer conditioning process.

As shown in FIG. 3F, the efficiency of the heat transfer increases whenthe gas pressure increases. However, the efficiency may not improve muchmore when the gas pressure approaches to a certain level, for example100 Pa or above in FIG. 3F. Therefore, in some embodiments, the gaspressure in the space between wafer 320 and conditioning plate 315 maybe in a range of 50 Pa to 5,000 Pa during conditioning of wafer 320 toprovide an efficient heat transfer while keeping the gas pressure levelsufficiently low. In some embodiments, the gas pressure may be in arange of 100 Pa to 1,000 Pa during conditioning of wafer 320 to providea balance between the heat transfer efficiency while keeping the gaspressure close to vacuum.

In some embodiments, gas 338 may be temperature conditioned so that thegas molecules themselves may provide heat transfer to wafer 320. Forexample, the gas supply, gas valves 370 and 375, or any other part ofload lock system 300 a may include a heater to precondition thetemperature of gas 338 before providing gas 338 into chamber 310.

In some embodiments, one or more gas vents 330 and 335 may be includedin load lock chamber 310 as shown in FIG. 3A. In other embodiments, suchas load lock system 300 b shown in FIG. 3B, at least one of gas vents(e.g. gas vent 330 in FIG. 3B) may be included in conditioning plate 315and provide gas 338 directly into the space between wafer 320 andconditioning plate 315. For example, in such embodiments, gas vent 330may be included in conditioning plate 315 and located at or near to thecenter of wafer 320. It is appreciated that gas vents may be located atany other places as long as the vents are suitable for providing gas 338into the space between wafer 320 and conditioning plate 315 in load lockchamber 310. It is also appreciated that load lock system 300 a and 300b may include any number of gas vents. In some embodiments, controller350 may be configured to adjust gas vents 330 or 335 to change the gasflow rate into load lock chamber 310.

FIG. 3C shows an exemplary graph showing a wafer temperature change overtime during wafer temperature conditioning in a load lock system. As theheat is transferred to the wafer, the temperature of wafer (T_(wafer))gradually approaches the temperature of wafer stage (T_(wafer stage)).The conditioning process may be completed when the wafer temperaturereaches a stable temperature (T_(stable)). In some embodiments,T_(stable) may be the same as the temperature of wafer stage. In otherembodiments, T_(stable) may be set to a point approximately 100 mK lowerthan the wafer stage temperature (T_(wafer stage)−100 mK) to provideefficient throughput improvement. In some embodiments, T_(stable) may bea setpoint at approximately 22° C. In other examples, T_(stable) may bea setpoint within a range of 20−28° C.

In some embodiments, as illustrated in FIG. 6C, when T_(wafer)approaches near to T_(stable), a controller (such as controller 350 inFIG. 3A) may adjust a heater (such as heater/cooler 360 in FIG. 3A) suchthat the conditioning plate temperature may be gradually reduced toprevent an overshoot of the wafer temperature.

After wafer 320 has reached T_(stable), the conditioning step isfinished, and thereafter the gas flow through gas vents (such as gasvents 330 and 335 in FIG. 3A) may be stopped. In some embodiments, afterstopping the gas flow, the load lock vacuum pump may continue to rununtil the pressure in the load lock chamber (such as load lock chamber310 in FIG. 3A) becomes at or near the pressure in the main chamber(such as main chamber 390 in FIG. 3A). Because the pressure inside theload lock chamber may have already been maintained close to a vacuum(e.g. 10-10,000 Pa), the pressure difference between the load lockchamber and the main chamber may be relatively small. In someembodiments, the heater (such as heater/cooler 360 in FIG. 3A) maymaintain the temperature of conditioning plate such that the residualradiation from the conditioning plate may help to keep the temperatureof wafer during the pump down.

When the gas pressure in the load lock chamber reaches at or near thepressure in the main chamber, in some embodiments, the wafer may betransported to the wafer stage (such as wafer stage 395 in FIG. 3A) forinspection. Because the temperature of the wafer may be at or near thetemperature of the wafer stage, the inspection can begin with a minimalwait period. In other embodiments, the wafer may be transported to aparking station (such as parking station 70 of FIG. 1B) and betemporarily stored until the on-going inspection of the previous waferis completed.

Reference is now made to FIG. 3D, which shows another exemplary loadlock system 300 d, consistent with embodiments of the presentdisclosure. In some embodiments, load lock system 300 d may include aplurality of supporting structures 325 and a conditioning plate 315configured to transfer heat to wafer 320. In some embodiments,conditioning plate 315 may include a heat transfer element 340.

In some embodiments, as illustrated in FIG. 3D, conditioning plate 315may be positioned above wafer 320. In such embodiments, wafer 320 issupported by supporting structures 325 coupled to a supporting plate319. While it is appreciated that more efficient heat transfer may beachieved as wafer 320 is positioned closer to conditioning plate 315, insome embodiments, it may be desirable to have sufficient distance inbetween wafer 320 and conditioning plate 315 to provide space for arobot arm to lift or transport wafer 320. In the configuration shown inFIG. 3D, however, because conditioning plate 315 is positioned abovewafer 320, conditioning plate 315 may be placed much closer to wafer320. In some embodiments, the distance may be reduced to approximately 1mm between wafer 320 and conditioning plate 315.

In some embodiments, load lock system 300 d may include gas vents 330and 335 to provide gas 338 to the space between wafer 320 andconditioning plate 315. In some embodiments, at least one gas vent maybe included in conditioning plate 315 to provide gas 338 to the space.It is appreciated that gas vents 330 or 335 may be located at otherplace of load lock system 300 d as long as those places are suitable forproviding gas 338 into the space between wafer 320 and conditioningplate 315 in load lock chamber 310. It is also appreciated that loadlock system 300 d may include any number of gas vents.

Reference is now made to FIG. 3E, which shows another exemplary loadlock system 300 e, consistent with embodiments of the presentdisclosure. Load lock system 300 e may include a plurality ofconditioning plates configured to transfer heat to wafer 320 frommultiple directions. For example, load lock system 300 e may include anupper conditioning plate 317 configured to transfer heat in a downwarddirection and a lower conditioning plate 318 configured to transfer heatin an upward direction. In some embodiments, upper conditioning plate317 may include a heat transfer element 340. In some embodiment, lowerconditioning plate may include a heat transfer element 340. Lowerconditioning plate 318 may be coupled to supporting structures 325configured to support wafer 320. Load lock system 300 e may include gasvents 330 and 335 to provide gas 338 to a space between wafer 320 andconditioning plates 317 and 318. In some embodiments, at least one gasvent may be included in upper conditioning plate 317. In someembodiments, at least one gas vent may be included in lower conditioningplate 318.

Reference is now made to FIG. 4, which is a schematic diagram of anexemplary pre-aligner in an equipment front end module (EFEM),consistent with embodiments of the present disclosure. In someembodiments, pre-aligner may include one or more supporting structures425 configured to support a wafer 420 and conditioning plate 415configured to transfer heat via heated compressed air from one or moreair vents 4140. In some embodiments, conditioning plate 415 furthercomprises one or more vacuum channel 450 configured to remove air. Insuch embodiments, heat transfer between wafer 420 and conditioning plate415 may be created mainly by convection via temperature conditionedcompressed air provided via one or more air vents 440. Because waferconditioning is performed through forced convection of the temperatureconditioned compressed air, the heat is transferred to or from wafer 420efficiently, and therefore the wafer temperature may stabilize quicklyto a stable temperature.

Reference is now made to FIG. 5, which shows a schematic diagramillustrating an exemplary configuration of a wafer conditioning system500, consistent with embodiments of the present disclosure. In someembodiments, wafer conditioning system 500 may include a plurality ofsupporting structures 525 and a conditioning plate 515 configured totransfer heat to wafer 520. Supporting structures 525, coupled toconditioning plate 515, may support wafer 520 and conduct heat to wafer520. It is appreciated that supporting structures 525 may be in anyshape suitable to support and conduct heat. In some embodiments,conditioning plate 515 may include a heat transfer element 540configured to change the temperature of conditioning plate 515, which inturn affects the temperature of wafer 520. Heat transfer element 540 maybe coupled to a heater 560. In some embodiments, heater 560 may beplaced outside of a vacuum chamber 510. In other embodiments, heater 560may be placed inside of vacuum chamber 510.

In some embodiments, conditioning plate 515 may further include anelectrostatic clamp 570. Electrostatic clamp 570 may hold wafer 520 toconditioning plate 515 via an electric charge. A power source (notshown) provides the electric charge connecting wafer 520 toelectrostatic clamp 570. For example, electrostatic clamp 570 may bepart of or comprised in the conditioning plate 515. In other examples,electrostatic clamp 570 may be separate to conditioning plate 515. Insome embodiments, conditioning plate 515 may include lifting structures526 configured to lift wafer 520 to accommodate robot arms (not shown)for transporting wafer 520.

In some embodiments, vacuum chamber 510 may include a heat transferelement 545 configured to change the temperature of vacuum chamber 510.In such embodiments, heat may be transferred from internal surfaces ofvacuum chamber 510 to wafer 520 via radiation (as illustrated in FIG.5). Vacuum chamber 510 may be a load lock chamber 20 of FIG. 1B, part ofparking station 70 of FIG. 1B, or main chamber 10 of FIG. 1B.

Reference is now made to FIG. 6A, which shows a schematic diagramillustrating another exemplary configuration of a wafer conditioningsystem 600, consistent with embodiments of the disclosure. System 600may include a vacuum chamber 610 and one or more supporting structures625 configured to support a wafer 620. In some embodiments, waferconditioning system 600 may include one or more of heating devicesconfigured to transfer heat to wafer 620 via radiation from multipledirections. For example, as shown in FIG. 6A, system 600 may includeupper heating device 617 and lower heating device 618.

In some embodiments, heating device 617 or 618 may be a conditioningplate, one or more tubes, or one or more coils configured to radiateheat to wafer 620. In some embodiments, system 600 may include a singleheating device, which may be positioned above or below wafer 620. Insome embodiments, system 600 may include upper heating device 617 andlower heating device 618 positioned relative to wafer 620. In someembodiments, system 600 may include three or more heating devices. Insome embodiments, system 600 may include a heater 660 configured toprovide heat to heating device 617 or 618. Heater 660, in someembodiments, may be a water heater or any other type of heater that canprovide heat to heating devices 617 or 618.

In some embodiments, supporting structure 625 may include a temperaturesensor 627 configured to measure the temperature of wafer 620.Temperature sensor 627 may comprise a thermocouple (TC), an NTCthermistor, a PTC thermistor, resistance thermometer, an infraredthermometer, or any other devices suitable for measuring the temperatureof wafer 620. For example, as shown in FIG. 6B, supporting structure 625may include a thermocouple configured to measure a temperature of wafer620. To enable measuring the temperature of wafer, supporting structure625 may include a spring-like structure to push the thermocouple to comeinto contact with wafer 620. In some embodiments, the thermocouple andthe spring-like structure may be enclosed by supporting structure 625.

Since system 600 operates in vacuum chamber 610, the heat transfer fromwafer to the thermocouple, for measurement of wafer temperature, may bevia conduction and radiation. For some embodiments, to measure thetemperature of wafer 620 more accurately, it may be desired to minimizethe heat radiation to the thermocouple. Accordingly, the surfaces of thethermocouple, except for the surface contacting wafer 620, may becovered by one or more structures made of a material that does nottransmit heat, such that the thermocouple may receive heat viaconduction from wafer 620. In some embodiments, supporting structure 625may be made of the material preventing heat transfer. In someembodiments, system 600 may include multiple thermocouples to collecttemperature information from multiple parts of wafer 620. In suchembodiments, a controller (such as controller 650 shown in FIG. 6E) maydetermine the temperature distribution characteristics of wafer 620.

Reference is now made to FIG. 6C, which is an exemplary graphillustrating temperature changes during the conditioning process. Awafer conditioning system may include a control mechanism to change thetemperature of heating devices on the fly while wafer conditioning is inprogress. Furthermore, in some embodiments, the wafer conditioningsystem may include one or more temperature sensors configured to measuretemperatures of various part of the system. In some embodiments, thewafer conditioning system may include one or more temperature sensorsconfigured to measure the temperature of the wafer itself. FIG. 6Cillustrates the temperature change over time in an example of suchembodiments. In such embodiments, it is possible to start theconditioning process with high temperatures of heating devices (evenhigher than the desired stable temperature, T_(stable)), and then bringthe temperatures down gradually to the desired stable temperature asT_(wafer) approaches T_(stable). In some embodiments, this process maybe further optimized by the temperature information from the sensors. Asshown in FIG. 6C, controlling the temperature in such way may reduce theconditioning time significantly.

Reference is now made to FIG. 6D, which is a schematic diagramillustrating an exemplary control circuit of a wafer conditioningsystem, consistent with embodiments of the present disclosure. In someembodiments, a wafer conditioning system, such as system 600 in FIG. 6A,may include a controller and one or more of temperature sensorsconfigured to measure various parts of the system. In some embodiments,the wafer conditioning system may include one or more temperaturesensors configured to measure the temperature of wafer. For example,controller 650 may receive temperature data about the temperature ofincoming wafer from a temperature sensor 696 in an equipment front endmodule (such as EFEM 30 of FIG. 1A). Controller 650 may receive wafertemperature data about the temperature of wafer from temperature sensor627. Controller 650 may receive heater temperature data about thetemperature of the output of heater 660 (e.g. water at the output of awater heater) from temperature sensor 665. In some embodiments,controller 650 may control heater 660 based on the at least one of thetemperature data from sensors 696, 627, and 665. For example, heater 660may comprise an electric water heater configured to transfer heat towater. With the temperature feedback, controller 650 may adjust theelectric current supplied to heater 660, thereby resulting in the changeof the temperature of heat transfer elements (e.g. heating devices 617or 618 in FIG. 6A). In some embodiments, controller 650 may becalibrated based on the types or conditions of wafer.

Even if the control mechanism is described in context of system 600 ofFIG. 6A to explain the functionality, it is appreciated that the samecontrol mechanism may be applied to any of the embodiments of waferconditioning system shown in this disclosure.

Reference is now made to FIG. 7, which is a flow chart illustrating anexemplary method for conditioning a wafer temperature, consistent withembodiments of the present disclosure. The method may be performed by aload lock system (e.g., load lock systems 300 a, 300 b, 300 d, and 300 eof FIGS. 3A-3D) of an e-beam system (e.g., charged particle beaminspection system 100 of FIG. 1A).

In step 710, a wafer is loaded by a robot arm into a load lock chamberrelative to a conditioning plate. In some embodiments, the wafer may beplaced above the conditioning plate. In other embodiments, the wafer maybe placed below the conditioning plate. In some embodiments, the wafermay be placed between two conditioning plates.

In step 720, after the wafer is loaded into a load lock chamber (e.g.,load lock chamber 20 in FIG. 1A), a controller (e.g. controller 50 ofFIG. 1A) enables a vacuum pump to remove air from the load lock chamber.

In step 730, the temperature of wafer stage (e.g. wafer stage 395 ofFIG. 3A) is determined and provided to the controller.

In step 740, a gas supply (e.g. gas supply in FIG. 3A) provides a gas tothe load lock chamber for heat transfer between the conditioning plateand the wafer. The gas may be temperature conditioned to match themeasured temperature of wafer stage to provide more efficient heattransfer.

In step 750, the controller receives the wafer stage temperature dataand adjusts the heating temperature based on the determined temperatureof the wafer stage.

In step 760, after the wafer conditioning is completed, the waferconditioning system transfers the conditioned wafer from the load lockchamber to a main chamber (e.g. main chamber 390 in FIG. 3A) or aparking station (e.g. parking station 70 in FIG. 3B). In someembodiments, if a temperature sensor is present to measure thetemperature of wafer, the controller may monitor the wafer temperatureand determine whether the wafer conditioning is completed.

It is appreciated that a controller of the wafer conditioning systemcould use software to control the functionality described above. Forexample, the controller may send instructions to the aforementionedheater to change the temperature of heat transfer elements. Thecontroller may also send instructions to adjust input voltage or currentto the heater. The software may be stored on a non-transitory computerreadable medium. Common forms of non-transitory media include, forexample, a floppy disk, a flexible disk, hard disk, solid state drive,magnetic tape, or any other magnetic data storage medium, a CD-ROM, anyother optical data storage medium, any physical medium with patterns ofholes, a RAM, a PROM, and EPROM, cloud storage, a FLASH-EPROM or anyother flash memory, NVRAM, a cache, a register, any other memory chip orcartridge, and networked versions of the same.

Reference is now made to FIGS. 8A and 8B, which show schematic diagramsillustrating an exemplary charged particle beam inspection system 800with a vacuum pump system, consistent with embodiments of the presentdisclosure. In some embodiments, charged particle beam inspection system800 may include a main chamber 890 and a load lock chamber 810. In someembodiments, system 800 may include a gas supply 811, gas vent valve812, and gas vent diffuser 813 that is connected to load lock chamber810. Gas supply 811 may provide a gas (e.g., gas 338 in FIG. 3A) intoload lock chamber 810 during wafer conditioning process to increasethermal conductivity between a wafer (e.g., wafer 320 of FIG. 3A) and aconditioning plate (e.g., conditioning plate 315 of FIG. 3A). The gasmay be nitrogen, helium, hydrogen, argon, CO2, or compressed dry air. Itis appreciated that the gas may be any other gas suitable for heattransfer.

In some embodiments, the vacuuming of load lock chamber 810 may beperformed over two stages via two separate paths. This first path iscalled a roughing path and may comprise a load lock roughing line 816and a load lock roughing valve 853. During the roughing stage, load lockchamber 810 is pumped down from the atmospheric condition to a “rough”vacuum level (e.g., 5×10⁻¹ Torr). In the first stage, load lock roughingvalve 853 is opened to initially pump down load lock chamber 810 viaload lock roughing line 816 while the other path is closed.

The second path is called a turbo pumping path and may comprise a loadlock turbo valve 814, a load lock turbo pump 815, a load lock turbopumping line 817, and a load lock turbo pump backing valve 851. Afterthe roughing of load lock chamber 810 is completed, load lock turbo pump815 takes over to pump out load lock chamber 810 to a deeper vacuumlevel (e.g., lower than 1.5×10⁻⁶ Torr). In this second stage, load lockroughing valve 853 is first closed. Then load lock turbo valve 814 andload lock turbo pump backing valve 851 are opened, so that load lockturbo pump 815 pumps down load lock chamber 810.

Main chamber 890 may be vacuumed in a similar way. First, main chamber890 is pumped down from the atmospheric condition to a “rough” vacuumlevel (e.g., 5×10⁻¹ Torr) via a main chamber roughing path (comprising amain chamber roughing line 896 and a main chamber roughing valve 854).After roughing stage is completed, a main chamber turbo pump 895 takesover to pump further down to a deeper vacuum level (e.g., lower than1.5×10⁻⁶ Torr) via a main chamber turbo pumping path (comprising a mainchamber turbo valve 894, a main chamber turbo pump 895, a main chamberturbo pumping line 897, and a main chamber turbo pump backing valve852). In some embodiments, main chamber turbo pump 895 may continue torun until the wafer inspection is completed.

While FIG. 8A shows system 800 having one roughing path and one turbopumping path for load lock chamber 810, it is appreciated that thesystem may utilize any number of roughing paths and turbo pumping pathsto vacuum load lock chamber 810. For example, system 800 may have two ormore roughing paths parallelly connected to load lock chamber 810.Independent from the number of roughing paths, system 800 may have twoor more turbo pumps parallelly connected to load lock chamber 810.Similarly, it is appreciated that the system may utilize any number ofroughing path and turbo pumping path to pump down main chamber 890.

In some embodiments, system 800 may include a central manifold box 850in which all roughing lines (e.g., load lock roughing line 816 and mainchamber roughing line 896) and all pumping lines (e.g., load lock turbopumping line 817 and main chamber turbo pumping line 897) are merged.Central manifold box 850 may house a number of valves to control thevacuuming process. For example, central manifold box 850 may includeload lock roughing valve 853, main chamber roughing valve 854, load lockturbo pump backing valve 851, and main chamber turbo pump backing valve852. After these individual valves, all lines are merged to a foreline858. The final exhaustion through a dry vacuum pump 860 is controlled bya foreline valve 859 that may be located before dry vacuum pump 860.

As described in the previous sections with respect to FIG. 3A, in someembodiments, during the wafer temperature conditioning process, loadlock chamber 810 may be continuously pumped down via roughing line 816or turbo pump 815 to continuously remove some of the gas molecules(e.g., gas 338 of FIG. 3A) and maintain the vacuum level of load lockchamber 810 until the wafer conditioning is completed.

As illustrated in FIG. 8B, in some embodiments, this continuous pumpingdown of load lock chamber 810 may introduce a temporary pressure jump inthe shared foreline (e.g., foreline 858), thereby causing the inspectionprocess in main chamber 890 to be interrupted. For example, as explainedin the previous sections, the wafer temperature conditioning process maybe performed in load lock chamber 810 at the same time a previous waferis being inspected in main chamber 890. When load lock roughing valve853 is opened to begin the continuous pumping down process, however, thepressure within foreline 858 may increase because the high-pressurecondition in load lock chamber 810 is exposed to foreline 858 due to theopen connection established through load lock roughing line 816. Theincreased pressure in foreline 858 may create higher back pressure tomain chamber turbo pump 895. Because main chamber turbo pump 895, insome embodiments, may be concurrently running to maintain low pressurelevel in main chamber during the inspection of the previous wafer whenthe wafer temperature conditioning is performed in load lock chamber810, the sudden increase of back pressure may influence the dynamicbehavior of turbo pump 895. As a result, a sudden vibration on system800 may occur. This sudden vibration may cause an inspection error.Therefore, if the vibration level is higher than a margin for theinspection error, the inspection process may need to be paused until theback pressure disappears and the vibration is damped. This interruptionof the inspection process may hurt the system throughput. The increasedback pressure may also cause the effective pumping speed of turbo pump895 decreased, thereby increasing the pressure in main chamber 890temporarily. This temporary increase of main chamber pressure may alsoimpact the system throughput and the overall system performance. Theeffects are explained in more details in the next section with respectto FIG. 9.

Reference is now made to FIG. 9, which an exemplary graph illustrating apressure change in a main chamber (e.g., main chamber 890 of FIGS. 8Aand 8B) of a charged particle beam inspection system (e.g., chargedparticle beam inspection system 800 of FIGS. 8A and 8B). As explainedabove with respect to FIG. 8A, the main chamber is pumped down over twostages, which are roughing stage 911 and turbo pumping down stage 912.During roughing stage 911, the main chamber is pumped down from theatmospheric condition to a “rough” vacuum level 910 (e.g., 5×10⁻¹ Torr)via the roughing path. After the main chamber pressure reaches “rough”vacuum level 910, a roughing valve (e.g., main chamber roughing valve854 of FIG. 8A) is closed and a main chamber turbo pump (e.g., mainchamber turbo pump 895) takes over to bring the main chamber pressurefurther down to a deeper vacuum level. When the main chamber pressurebecomes lower than an “inspection ready” vacuum level 920 (e.g.,1.5×10⁻⁶ Torr), the wafer inspection process may begin. In someembodiments, main chamber turbo pump 895 may continue to run to maintainmain chamber pressure level close to “inspection ready” level 920.

When the inspection of a first wafer is completed, in some embodiments,the wafer exchange may occur in a period 923. During wafer exchange, themain chamber pressure may increase temporarily because the gate valve(e.g., gate valve 26 of FIG. 1B) between a load lock chamber (e.g., loadlock chamber 810 of FIG. 8A) and the main chamber (e.g., main chamber890 of FIG. 8A) is opened. After the wafer exchange, the inspectionprocess may begin again once the main chamber turbo pump brings the mainchamber pressure back down to “inspection ready” vacuum level 920.

Before the wafer exchange, while the first wafer is being inspected inthe main chamber, the second wafer may go through the wafer temperatureconditioning process, and as explained above, the main chamber pressuremay temporarily increase due to the back pressures applied to the mainchamber turbo pump. An example of the temporary pressure jump 950 isillustrated in the graph.

If the temporary pressure jump 950 is still below “inspection ready”vacuum level 920, the inspection of the first wafer may continue withoutan interruption as long as the vibration level stays within the marginof error. However, if the main chamber pressure increases higher than“inspection ready” vacuum level 920 during the temporary jump 950, theinspection of the first wafer may need to be paused until the mainchamber pressure comes back down to “inspection ready” level. As aresult, the system throughput may be impacted by this interruption.

Reference is now made to FIG. 10, which shows a schematic diagramillustrating an exemplary charged particle beam inspection system 1000with an improved vacuum pump system, consistent with embodiments of thepresent disclosure. In some embodiments, a separate pumping path may beadded to a load lock chamber 810 to prevent the vibration and thepressure jump in a main chamber 890. For example, in some embodiments,charged particle beam inspection system 1000 may include a load lockbooster roughing valve 1010, a load lock booster roughing pump 1011, andan auxiliary exhaust system 1012. All other part of system 1000 are thesame as system 800 of FIG. 8A.

In such embodiments, during the wafer temperature conditioning, loadlock booster roughing pump 1011 may continuously run to remove the gasmolecules (e.g., gas 338 of FIG. 3A). However, because load lockroughing valve 853 and load lock turbo pump backing valve 851 remainclosed during this period, there is no pressure increase in foreline858, hence no back pressure may be incurred on main chamber turbo pump895.

Accordingly, in some embodiments, pumping down process for load lockchamber 810 may be broken down to three stages. First, load lock boosterroughing pump 1011 may operate from the atmospheric condition (afterreceiving a new set of wafers from EFEM (e.g., EFEM 30 of FIG. 1A) to avacuum level for wafer temperature conditioning. Second, the regularload lock roughing path (via load lock roughing line 816) may operatefrom the wafer temperature conditioning vacuum level to the “rough”vacuum level. Finally, load lock turbo pump 815 may operate from the“rough” vacuum level to the deeper vacuum level. The back pressureproblem is the highest when foreline 858 is exposed to the viscousregime in the beginning of pumping near the atmospheric condition. As aresult, after the load lock chamber pressure level is brought down to awafer temperature conditioning vacuum level by the separate booster pump(e.g., load lock booster roughing pump 1011), the regular pumpingmechanisms (e.g., load lock roughing line 816 or load lock turbo pump815) can be used without creating too much hack pressure.

Reference is now made to FIG. 11, which is a flow chart illustrating anexemplary method for controlling vacuum level of a load lock chamber ofthe charged particle beam inspection system of FIG. 10, consistent withembodiments of the present disclosure. The method may be performed bythe charged particle beam inspection system of FIG. 10.

In step 1110, a wafer (or a plurality of wafers) is loaded by a robotarm (e.g., robot arm 11 of FIG. 1B) into a load lock chamber (e.g., loadlock chamber 810 of FIG. 10).

In step 1111, a gas supply (e.g. gas supply 811 of FIG. 10) startsproviding a gas (e.g., gas 338 of FIG. 3A) to the load lock chamber forthe wafer temperature conditioning.

In step 1112, all gates (e.g., gate valve 25 and 26 of FIG. 1B) areclosed in preparation of the vacuuming process. In some embodiments,step 1111 may occur after all gates are closed in step 1112.

In step 1113, a booster pump valve (e.g., load lock booster roughingvalve 1010) is opened and a booster pump (e.g., load lock boosterroughing pump 1011) starts pumping down the load lock chamber. Asexplained above with respect to FIG. 10, in this first stage, the loadlock chamber is pumped down from the atmospheric condition to a vacuumlevel suitable for wafer temperature conditioning. Because the boosterpumping line is connected to a separate exhaust system (e.g., auxiliaryexhaust system 1012 of FIG. 10) and not merged with the regular roughingpaths to form a shared foreline (e.g., foreline 858 of FIG. 10) in amanifold box (e.g., central manifold box 850 of FIG. 10), the boosterpumping does not cause back pressure in the foreline. Therefore theremay be no impact on the system throughput.

In step 1114, the wafer conditioning flow starts. This step may includeadjusting the heating temperature of a conditioning plate (e.g.,conditioning plate 315 of FIG. 3A) based on the determined temperatureof the wafer stage (e.g., wafer stage 395 of FIG. 3A) in a main chamber(e.g., main chamber 890 of FIG. 10). While wafer temperatureconditioning is performed, the booster pump continues to run to maintainthe vacuum level suitable for wafer temperature conditioning. In step1115, when the wafer temperature reaches a stable temperature (e.g.,T_(stable) in FIG. 3C), the conditioning process is completed.

In step 1116, after the wafer temperature conditioning is completed, agas vent valve (e.g., gas vent valve 812 of FIG. 10) is closed and thegas supply is stopped. In step 1117, the first stage of pumping downprocess is completed and the booster valve (e.g., load lock boosterroughing valve 1010) is closed.

In step 1118, the second stage of pumping down process begins by openinga load lock roughing valve (e.g., load lock roughing valve 853 of FIG.10). During this second stage, the load lock chamber in some embodimentsmay be pumped down from the wafer conditioning vacuum level to a “rough”vacuum level (e.g., 5×10−1 Torr). After reaching the “rough” vacuumlevel, in step 1119, the load lock roughing valve is closed.

In step 1120, the third stage of pumping down process begins and a turbopump (e.g., load lock turbo pump 815) takes over to pump out load lockchamber 810 to a deeper vacuum level close to the main chamber pressure.

In step 1121, after the wafer inspection for the previous wafer iscompleted, the previous wafer is removed from the main chamber and thetemperature conditioned wafer is transferred from the load lock chamberto the main chamber. In step 1122, when the wafer exchange is completed,the load lock turbo pump valve is closed.

After step 1122, step 1110 can be performed to load a new set of wafersto the load lock chamber. If an unconditioned and uninspected wafer isstill present in the load lock chamber, the system may proceed to step1111 to condition another wafer in preparation of the inspectionprocess.

It is appreciated that a controller of the wafer conditioning systemcould use software to control the functionality described above. Forexample, the controller may send instructions to the aforementionedvalves and pumps to control the pumping down paths. The software may bestored on a non-transitory computer readable medium. Common forms ofnon-transitory media include, for example, a floppy disk, a flexibledisk, hard disk, solid state drive, magnetic tape, or any other magneticdata storage medium, a CD-ROM, any other optical data storage medium,any physical medium with patterns of holes, a RAM, a PROM, and EPROM,cloud storage, a FLASH-EPROM or any other flash memory, NVRAM, a cache,a register, any other memory chip or cartridge, and networked versionsof the same.

The embodiments may further be described using the following clauses:

1. A load lock system, comprising:

a plurality of supporting structures configured to support a wafer;

a first conditioning plate including a first heat transfer elementconfigured to adjust a temperature of the wafer;

a first gas vent configured to provide a gas between the firstconditioning plate and the wafer; and

a controller including a processor and a memory, the controllerconfigured to assist with control of the first heat transfer element.

2. The load lock system of clause 1, wherein the first conditioningplate is positioned above the wafer.

3. The load lock system of clause 1, wherein the first conditioningplate is positioned below the wafer.

4. The load lock system of clause 3, wherein the plurality of supportingstructures are coupled to the first conditioning plate.

5. The load lock system of any one of clauses 1-4, wherein the first gasvent is attached to the first conditioning plate.

6. The load lock system of any one of clauses 1-5, wherein thecontroller is further configured to assist with the control of the firstheat transfer element based on a temperature of a wafer stage.

7. The load lock system of any one of clauses 1-6, wherein thecontroller is further configured to control a rate of gas flow throughthe first gas vent.

8. The load lock system of any one of clause 1-7, further comprising asecond conditioning plate including a second heat transfer elementconfigured to adjust the temperature of the wafer.

9. The load lock system of clause 8, wherein the plurality of supportingstructures configured to support a wafer are positioned between thefirst conditioning plate and the second conditioning plate.

10. The load lock system of clause 9, further comprising a second gasvent configured to provide a portion of the gas between the secondconditioning plate and the wafer.

11. The load lock system of clause 10, wherein the second gas vent iscoupled to the second conditioning plate.

12. The load lock system of any one of clauses 8-11, wherein thecontroller is further configured to assist with controlling the secondheat transfer element based on a temperature of the wafer stage.

13. The load lock system of any one of clauses 10-12, wherein thecontroller is further configured to control a rate of gas flow throughthe second gas vent.

14. The load lock system of any one of clauses 1-13, wherein the gascomprises nitrogen, helium, hydrogen, argon, CO2, or compressed air.

15. The load lock system of any one of clauses 1-14, further comprisinga load lock chamber configured to enclose the first conditioning plate,the plurality of supporting structures, and the wafer.

16. The load lock system of clause 15, further comprising a first vacuumpump connected to the load lock chamber.

17. The load lock system of clause 16, wherein the controller is furtherconfigured to control the first vacuum pump to pump out the gas during awafer conditioning process.

18. The load lock system of clause 17, wherein the controller is furtherconfigured to maintain a pressure inside of the load lock chamber in arange of 50 to 5,000 Pa during the wafer conditioning process.

19. The load lock system of any one of clauses 16-18, further comprisinga second vacuum pump connected to the load lock chamber.

20. The load lock system of clause 19, wherein the controller is furtherconfigured to:

enable the first vacuum pump to reduce pressure inside of the load lockchamber to a first pressure level, and

enable the second vacuum pump to reduce pressure inside of the load lockchamber to a second pressure level, wherein the second pressure level islower than the first pressure level.

21. The load lock system of clauses 20, wherein the second vacuum pumpshares an exhaust path with a third vacuum pump connected to a mainchamber.

22. The load lock system of any one of clauses 20 and 21, wherein thesecond vacuum pump is disabled while the first vacuum pump is enabled.

23. The load lock system of any one of clauses 20-22, wherein the firstvacuum pump and the third vacuum pump are concurrently enabled.

24. A method of conducting a thermal conditioning of a wafer in a loadlock system, comprising:

loading a wafer to a load lock chamber of a load lock system;

pumping down the load lock chamber;

providing a gas to the load lock chamber; and

enabling a first heat transfer element in a first conditioning plate toadjust a temperature of the first conditioning plate for transferringheat through the gas to the wafer.

25. The method of clause 24, wherein providing a gas to the load lockchamber further comprises conditioning a temperature of the gas beforeproviding the gas to the load lock chamber.

26. The method of any one of clauses 24 and 25, wherein providing a gasto the load lock chamber further comprises providing the gas to a spacebetween the first conditioning plate and the wafer.

27. The method of any one of clauses 24-26, further comprisingdetermining a temperature of a wafer stage in a main chamber.

28. The method of any one of clauses 24-27, wherein enabling the firstheat transfer element to adjust the temperature of the firstconditioning plate further comprises adjusting the first heat transferelement based on the determined temperature of the wafer stage.29. The method of any one of clauses 24-28, further comprising enablinga second heat transfer element in a second conditioning plate to adjusta temperature of the second conditioning plate for transferring heatthrough the gas to the wafer.30. The method of any one of clauses 24-29, wherein the gas comprisesnitrogen, helium, hydrogen, argon, CO2, or compressed air.31. The method of any one of clauses 24-30, wherein pumping down theload lock chamber comprises pumping the gas out of the load lock chamberusing a first vacuum pump connected to the load lock chamber.32. The method of clause 31, wherein pumping down the load lock chamberfurther comprises:

enabling the first vacuum pump to reduce pressure inside of the loadlock chamber to a first pressure level; and

enabling a second vacuum pump connected to the load lock chamber toreduce pressure inside of the load lock chamber to a second pressurelevel, wherein the second pressure level is lower than the firstpressure level.

33. The method of clauses 32, wherein the second vacuum pump shares anexhaust path with a third vacuum pump connected to the main chamber.

34. The method of any one of clauses 32 and 33, wherein the secondvacuum pump is disabled while the first vacuum pump is enabled.

35. The method of any one of clauses 32-34, wherein the first vacuumpump and the third vacuum pump are concurrently enabled.

36. A non-transitory computer readable medium including a set ofinstructions that is executable by one or more processors of acontroller to cause the controller to perform a method conducting athermal conditioning of a wafer, the method comprising:

instructing a first vacuum pump to pump down a load lock chamber of aload lock system after a wafer is loaded into the load lock chamber;

instructing a gas supply to provide a gas to the load lock chamber; and

instructing a first heat transfer element in a first conditioning plateto adjust a temperature of the first conditioning plate for transferringheat through the gas to the wafer.

37. The computer readable medium of clause 36, wherein the set ofinstructions that is executable by the one or more processors of thecontroller to cause the controller to further perform:

instructing a temperature sensor to determine a temperature of a waferstage in a main chamber.

38. The computer readable medium of clause 37, wherein instructing thefirst heat transfer element in the first conditioning plate furthercomprises adjusting the first heat transfer element based on thedetermined temperature of the wafer stage.

39. The computer readable medium of any clauses 36-38, wherein the setof instructions that is executable by the one or more processors of thecontroller to cause the controller to further perform:

instructing a second heat transfer element in a second conditioningplate to adjust a temperature of the second conditioning plate fortransferring heat through the gas to the wafer.

40. The computer readable medium of clause 39, wherein instructing thesecond heat transfer element in the second conditioning plate furthercomprises adjusting the second heat transfer element based on thedetermined temperature of the wafer stage.

41. The computer readable medium of any clauses 36-40, wherein the setof instructions that is executable by the one or more processors of thecontroller to cause the controller to further perform:

instructing the first vacuum pump to pump down the load lock chamber toa first pressure level; and

instructing a second vacuum pump to pump down the load lock chamber to asecond pressure level, wherein the second pressure level is lower thanthe first pressure level.

42. A method of pumping down a load lock chamber, the method comprising:

pumping a gas out of the load lock chamber with a first vacuum pumpconfigured to exhaust the gas to a first exhaust system; and

pumping the gas out of the load lock chamber with a second vacuum pumpconfigured to exhaust the gas to a second exhaust system.

43. The method of clause 42, further comprising:

enabling the first vacuum pump to reduce pressure inside of the loadlock chamber to a first pressure level; and

enabling the second vacuum pump to reduce pressure inside of the loadlock chamber to a second pressure level, wherein the second pressurelevel is lower than the first pressure level.

44. The method of clause 43, wherein the second vacuum pump shares thesecond exhaust system with a third vacuum pump configured to pump down amain chamber.

45. The method of any one of clauses 42-44, wherein the second vacuumpump is disabled while the first vacuum pump is enabled.

46. The method of any one of clauses 44-45, wherein the first vacuumpump and the third vacuum pump are concurrently enabled.

Although the disclosed embodiments have been explained in relation toits preferred embodiments, it is to be understood that othermodifications and variation can be made without departing the spirit andscope of the subject matter as hereafter claimed.

What is claimed is:
 1. A load lock system, comprising: a plurality ofsupporting structures configured to support a wafer; a firstconditioning plate including a first heat transfer element configured toadjust a temperature of the wafer; a first gas vent configured toprovide a gas between the first conditioning plate and the wafer; and acontroller including a processor and a memory, the controller configuredto assist with control of the first heat transfer element to conditionthe wafer before the wafer is transferred from the load lock system to amain chamber for inspection.
 2. The load lock system of claim 1, whereinthe first conditioning plate is positioned above the wafer.
 3. The loadlock system of claim 1, wherein the first conditioning plate ispositioned below the wafer.
 4. The load lock system of claim 1, whereinthe plurality of supporting structures are coupled to the firstconditioning plate.
 5. The load lock system of claim 1, wherein thefirst gas vent is included in the first conditioning plate.
 6. The loadlock system of claim 1, wherein the controller is further configured toassist with the control of the first heat transfer element based on atemperature of a wafer stage.
 7. The load lock system of claim 1,further comprising a second conditioning plate including a second heattransfer element configured to adjust the temperature of the wafer. 8.The load lock system of claim 7, wherein the plurality of supportingstructures configured to support a wafer are positioned between thefirst conditioning plate and the second conditioning plate.
 9. The loadlock system of claim 7, further comprising a second gas vent configuredto provide a portion of the gas between the second conditioning plateand the wafer.
 10. The load lock system of claim 7, wherein thecontroller is further configured to assist with controlling the secondheat transfer element based on a temperature of the wafer stage.
 11. Theload lock system of claim 1, further comprising a load lock chamberconfigured to enclose the first conditioning plate, the plurality ofsupporting structures, and the wafer.
 12. The load lock system of claim11, further comprising a second vacuum pump connected to the load lockchamber.
 13. The load lock system of claim 12, wherein the controller isfurther configured to: enable the first vacuum pump to reduce pressureinside of the load lock chamber to a first pressure level, and enablethe second vacuum pump to reduce pressure inside of the load lockchamber to a second pressure level, wherein the second pressure level islower than the first pressure level.
 14. The load lock system of claim13, wherein the second vacuum pump shares an exhaust path with a thirdvacuum pump connected to a main chamber.
 15. A non-transitory computerreadable medium including a set of instructions that is executable byone or more processors of a controller to cause the controller toperform a method conducting a thermal conditioning of a wafer, themethod comprising: instructing a first vacuum pump to pump down a loadlock chamber of a load lock system after a wafer is loaded into the loadlock chamber; instructing a gas supply to provide a gas to the load lockchamber; and instructing a first heat transfer element in a firstconditioning plate to adjust a temperature of the first conditioningplate for transferring heat through the gas to the wafer to conditionthe wafer before the wafer is transferred from the load lock chamber toa main chamber for inspection, the gas being provided between the firstconditioning plate and the wafer.